1. Field of the Invention
The present invention relates to a semiconductor technology in general. In particular, it relates to a method for forming on a semiconductor substrate a silicon insulation film offering low dielectric constant and achieving high material utilization by using a plasma CVD (chemical vapor deposition) apparatus.
2. Description of the Related Art
The demand for higher, more densely wired semiconductors in recent years is creating a need to reduce inter-wire volumes to prevent signal delays in devices that adopt multi-layer wiring technology. To reduce inter-wire volumes, it is necessary to reduce the dielectric constant of the insulation film formed between adjacent layers in a multi-layer wiring structure. Accordingly, development effort has been made to provide insulation films offering low dielectric constants.
The conventional silicon oxide film SiOx is formed by adding to a silicon material gas such as SiH4 or Si(OC2H5)4 an oxidizing agent being oxygen O2, nitric oxide NO or nitrous oxide N2O, and then heating or applying plasma energy to the mixture. The silicon oxide film obtained in this manner has heretofore offered a dielectric constant ε of approx. 4.0. On the other hand, the spin-coat method using an inorganic silicon oxide glass (SOG) material has made it possible to form an insulation film offering a low dielectric constant ε of approx. 2.3.
Also, the plasma CVD method, when CxFyHz is used as a material gas, has enabled the formation of a fluorinated amorphous carbon film with a low dielectric constant ε of 2.0 to 2.4. When a silicon hydrocarbon (such as P-TMOS (phenyl trimethoxy silane)) is used as a material gas, on the other hand, the plasma CVD method has been shown to form an insulation film with a low dielectric constant ε of 3.1. Furthermore, it has been made possible to form an insulation film with a low dielectric constant ε of approx. 2.5 under the plasma CVD method when a silicon hydrocarbon containing multiple alkoxyl groups is used as a material gas and the film forming conditions are optimized.
In addition, U.S. Pat. No. 6,846,515 describes a method for forming an insulation film of low dielectric constant using a porogen gas, wherein the deposited insulation film is cured to create pores in the film.